Active-matrix FPDs (Flat Panel Displays), which are driven by thin film transistors with amorphous-silicon or polycrystalline-silicon channel layers, are the mainstream of general FPDs.
Production of high-quality amorphous silicon or polycrystalline silicon requires high deposition temperatures of 300° C. or thereabout. For this reason, in order to fabricate flexible devices, very expensive, high water-absorption films, i.e. films that are difficult to work with, including high thermal-resistance polyimide films must be used as their substrates.
In recent years, thin film transistors using organic semiconductor materials have been studied actively.
Because such organic semiconductor materials can be produced in a printing process without using a vacuum process, they can be potentially produced at reduced cost. Organic semiconductor materials also have an advantage that they can be mounted on a flexible plastic substrate.
However, the organic semiconductor materials have a very low mobility, and a low resistance to aging, so they have not been widely used.
In these circumstances, metal oxide semiconductor materials, which can be formed at low temperatures, have been in the spotlight recently.
A thin film transistor, which is produced by forming an amorphous InGaZnO material, an example of a metal oxide semiconductor material formable at low temperatures, on a PET (polyethylene terephthalate) substrate as a channel layer, has excellent characteristics including a mobility of 10 cm2/Vs or thereabout, which is disclosed in the non-patent document 1.
Transistors having such a high mobility can be fabricated at room temperature, making it possible to form transistors on inexpensive and widely available plastic substrates, such as PET. This results in heightened expectations for widespread use of light and durable flexible displays.